This document discusses the electrophysiological evaluation of the brachial plexus using nerve conduction studies and electromyography. It describes the anatomy of the brachial plexus including its roots, trunks, divisions, cords, and terminal nerves. It explains how to assess each element of the brachial plexus using sensory nerve action potentials, compound muscle action potentials, and electromyography findings. It also discusses the patterns seen with different types of brachial plexus lesions and provides guidance on timing of electrodiagnostic testing and prognostication.

1. Electrophysiology topic
EDX evaluation of brachial plexus-An
approach

2. Brachial plexus
• One of the most complex and largest PNS
structure
• Highly vulnerable
• Extensive non routine NCS
• Time consuming
• Contra lateral asymptomatic limb also
needs to be studied

4. Anatomy
• 100,000-160,000 nerve fibers
• Intermingle to form various brachial plexus
elements
• Roots
• Trunks
• Divisions
• Cords
• Terminal nerves

6. Roots
• Dorsal and ventral rootlets, dorsal and ventral
roots, mixed spinal nerve in inter vertebral
foramina, posterior primary rami and anterior
primary rami
• Surgeons VS anatomists
• C5,C6,C7,C8,T1
• Prefixed, Post fixed
• Cannot be studied by per cutaneous stimulation
• Nerves arising from roots-dorsal scapular, long
thoracic,phrenic

8. Trunks
• Named after their relationship to one
another
• C5-C6 APR-upper trunk
• C7-middle trunk
• C8-T1-lower trunk
• Nerves from proximal upper trunk-
suprascapular, nerve to subclavius
• Mid and distal trunks can be stimulated in
supraclavicular fossa and axilla

10. Divisions and cords
• Each trunk divides into two. lie behind clavicle
• Lateral cord-anterior divisions of upper and
middle trunk C5-7roots
• Medial cord-continuation of anterior division of
lower trunk C8-T1roots
• Posterior cord-posterior division of all trunks C5-
C8 roots
• Cord elements can be stimulated
percutaneously

12. Nerves from cords
• Lateral cord-lateral pectoral, musculo
cutaneous, lateral head of median, lateral ante
brachial cutaneous.
• Posterior cord-sub scapular, thoraco dorsal,
axillary, radial
• Medial cord-medial pectoral, medial ante
brachial cutaneous, medial brachial cutaneous,
medial head of median nerve, ulnar
• Terminal nerve elements can be studied by
percutaneous stimulation

14. Classification of brachial plexus
lesion
• Supra clavicular VS infra clavicular
• Supra clavicular-commoner, severe and
worse prognosis
Upper plexus-better, conduction block,
proximity to muscles, extra foraminal and
repairable
Lower plexus-worse, axon loss, foraminal
lesions, distal far muscles

15. EDX manifestations of
pathophysiology
• Axon loss
• Demyelinative-conduction block or conduction
slowing
Good prognosis.
stimulation site dependent
distal to lesion –normal NCS
proximal stimulation-axilla and erb’s point
weak muscle, N cmap-EMG shows MUP dropout

16. Axon loss lesions
• Most common
• Wallerian degeneration 2-3 days later
• Decreased SNAP,CMAP amplitude, norm
al distal latencies and conduction
velocities
• Needle EMG-fibrillation potentials, MUP
drop out (High innervation ratio in limbs)

17. Severity of lesion
• CMAP amplitudes correlate well with
amount of axonal loss in one to one ratio
• Minimal lesion-EMG fibrillations
Normal SNAP,CMAP
• More severe-SNAP amps decrease
• Greater severity-absent SNAP,CMAP amp
decreased, MUP dropout

18. Timing of EDX
• MUP dropout-immediately but severe
• CMAP amps-begin to decrease on day 2-
3,reach nadir by day -7
• SNAP amp-begins to drop on day 6 and
reach nadir on day 10-11
• Fibrillation potentials-may take10- 21 days
to appear

19. Prognostication
• Re innervation is by collateral sprouting and
proximo distal regeneration
• Depends on grade and completeness of injuries,
distance between site of injury and innervated
muscle
• Regeneration is at 1 inch/month, denervated
muscle fibers survive for 18-24 months. so
distance more than 2 feet bad prognosis
• Reinnervation normalises CMAP amps but alters
morphology and recruitment

20. prognosis
• No time limit for sensory nerve
regeneration
• End organs of sensory nerve fibers donot
undergo degeneration
• Reinnervation successful even after two
years
• SNAP amplitude decrement correlates
well with sensory loss

21. SNAPs -importance
• Sensory fibers are more sensitive to axon loss
than motor fibers. Isolated SNAPs abnormalities
do not rule our motor axon involvement
• Intra spinal lesions do not affect sensory
conduction. but affect motor NCS and EMG
• Pattern of sensory loss localises lesion to
brachial plexus elements much before motor
NCS.
• Motor anormalities with normal SNAPs are seen
in-myopathies, preganglionic lesions, NMJ, early
GBS, study before 6 days

22. EDX assessment of brachial plexus
• Each brachial plexus element has-
Muscle domain/EMG domain
SNAP domain
CMAP domain
Domains of a distal element is sum of
domains of all elements forming it minus
domains of elements departing prior to
formation of the element

23. Root domains
• C5 APR- no SNAP domain
CMAP domain-Musc-biceps,
Ax-deltoid
EMG domain-C5 myotome
• C6 APR-SNAP domain-LABC(100%),Med-
D1(100%),s-radial(60%),Med-D2(20%),Med-
D3(10%)
CMAP domain-Musc-biceps, Ax-deltoid
EMG domain-C6 myotome

24. Root domains
• C7 APR:SNAP- Med-D2(80%),Med-D3(70%),S-
radial(40%)
No dependable CMAP domain
EMG-C7 myotome
• C8 APR:SNAP domain uln-D5
CMAP domain: uln-ADM, uln-FDI, Rad- EIP, Med-APB
EMG –C8 myotome
• T1 APR:SNAP-MABC
CMAP-Med-APB plus C8 cmap

28. EMG domains
• Upper trunk-(C5 plus C6) minus dorsal scapular,
long thoracic nerve.
• Middle trunk-C7 domain minus serratus anterior
• Lower trunk-C8 plus T1 APR
• Lateral cord-upper and middle trunks minus
supra scapular, subscapular, thoraco dorsal,
radial, axillary nerve
• Posterior cord-sum of sub scapular, thoraco
dorsal ,axillary and radial
• Medial cord-lower trunk minus posterior division
elements

29. Nerve domains
• Axillary nerve-no SNAP domain
CMAP domain: AX-deltoid
EMG :innervated muscles
• Musculo cutaneous: SNAP-LABC
CMAP domain: AX-deltoid
EMG-
• Radial :SNAP-s radial
CMAP: Rad-EDC,nRad-EIP
EMG-radial and posterior interossei

30. Nerve domains
• Median :SNAP domain- Med-D1,Med-
D2,Med-D3
CMAP domain-Med-APB
• Ulnar nerve: SNAP domain-Uln-D5
CMAP domain-uln-ADM,
uln-FDI.

33. Thank you